1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device including a process of removing foreign substances such as reaction product, which is formed on an inner wall of a trench when the trench is formed, with a cleaning solution after the trench is formed.
2. Description of the Related Art
Conventionally, a reactive ion etching (RIE) is used as a method of processing a trench to a semiconductor substrate. However, a trench having a higher aspect ratio is desired and a new trench processing technique such as so-called BOSCH process has been developed. The BOSCH process is a method of forming a trench having a high aspect ratio by digging a bottom of the trench while covering a sidewall of the trench with a protection layer. The BOSCH process using high density plasma such as inductive coupling plasma (ICP) and electron cyclotron resonance (ECR) enables processing of a trench having an aspect ratio of 50 or higher. Then, after forming the trench, a cleaning technique that can certainly remove foreign substances such as a reaction product formed on an inner wall of the trench when the trench is formed is required. The aspect ratio is a ratio of a depth of a trench to an opening width of the trench.
JP-A-2009-141307 discloses a method in which a mixed solution of sulfuric acid and hydrogen peroxide water is used as a cleaning solution. However, in a case where the mixed solution of sulfuric acid and hydrogen peroxide water is used as the cleaning solution, the following problems arise. (I) Because the mixed solution has a high viscosity, the mixed solution cannot be supplied to a bottom of a trench. (II) A lift-off effect of floating foreign substances such a reaction product existing in a trench is not achieved. (III) Although it is required to perform ultrasonic cleaning in order that a mixed solution having a high viscosity penetrates to a bottom of a trench, the ultrasonic cleaning cannot be performed because fine structure will be damaged. (IV) An effect of preventing condensation of foreign substances and an effect of preventing reattachment of foreign substances to an inner wall of a trench cannot be achieved.
JP-A-2006-319282 discloses a method in which a mixed solution of hydrogen peroxide water, ammonia water, and water is used as a cleaning solution. However, in a case where the mixed solution of hydrogen peroxide water, ammonia water, and water is used as the cleaning solution, the following problems arise. (I) An effect of preventing condensation of foreign substances and an effect of preventing reattachment of foreign substances to an inner wall of a trench cannot be achieved. (II) Foreign substances in the vicinity of a bottom of a trench may be reattached to an inner wall of the trench. (III) Although ultrasonic cleaning is effective to prevent reattachment, the ultrasonic cleaning cannot be performed because fine structure will be damaged.
Thus, in cases where the above-described cleaning solutions are used, there is a possibility that foreign substances cannot be removed with certainty to a bottom of a trench having a high aspect ratio.